This new volume of What's Happening in the Mathematical Sciences features a rich selection of articles about recent topics in pure and applied mathematics.

"Expanding Horizons" and "Needles in an Infinite Haystack" explain new developments in the theory of expander graphs and in number theory (asymptotic Fermat's last theorem), respectively. "The SetR Game Has Met Its Match" presents a solution of the so-called Cap Set Conjecture, a statement about arithmetic progressions in finite vector spaces, which resulted from the mathematical analysis of the popular game "Set".

"The Shape of Data" and "Quantum Computers and Golden Gates" present recent advances in theoretical computer science and related areas of data science. The mathematical aspects of one of the most fascinating recent developments in general relativity, the discovery of gravitational waves, is discussed in "When Black Holes Collide".

Three articles talk about applications of mathematical methods in various aspects of everyday life: bike-sharing systems and ride-sharing services (like Lyft and Uber) in "The Mathematics of Commuting", weight control in "The Calculus of Calories", and an analysis of various partisan election practices in "Gerrymandering: Mathematics on Trial".

We anticipate that many readers will find an interesting topic to read about and, hopefully, more than one.